1. Field of the Invention
The invention relates to a deriving system for deriving a center channel signal from a stereophonic signal comprising a left and a right channel signal. The use of a center channel signal in stereophonic sound reproduction has the effect that the position of the perceived virtual sound sources is less dependent on the position taken up by the listener relative to the left and right loudspeakers. This is especially important in the case where the reproduction of stereophonic audio information is combined with image reproduction, as is the case, for example, with TV comprising stereophonic sound reproduction. For, when a reproduced audio visual program is followed, it is important that the position of the perceived virtual sound sources is not perceived to be far from the position of the picture screen.
2. Description of the Related Art
A system for deriving a center channel signal is known from U.S. Pat. No. 4,024,344.
In the system described in that Patent, there is detected whether the low-frequency portions of the left and the right channel signal include correlated signal components. When this is detected, the low-frequency signal components in the left channel signal are multiplied by the low-frequency components in the right channel signal. The DC components of the result of the multiplication is compared with the sum of the DC components of the rectified channel signals.
Depending on the result of the comparison, a larger or smaller part of the sum of low-frequency components of the left and the right channel signal is used as a center channel signal.
The disadvantage of prior-art system is that in the center channel signal, the left and right channel signals are both represented equally strongly. This means that opposite-phase signal components in the left and right channel signals disappear in the thus obtained center channel signal. This is especially detrimental in the case where the opposite-phase components come from the most powerful sound source in the stereophonic signal. The disappearance of the opposite-phase components when the left and right channel signals are added up with an equal weight factor is one of the reasons why the listener experiences the thus obtained center channel signal as sounding dull.